A physician places a stent into a human blood vessel in response to several different types of conditions, including a weakening or rupture of the blood vessel or a narrowing of the vessel. The stent is intended to maintain a leak-free channel through the vessel for blood flow. The stent is made of biocompatible materials because it is in direct contact with an inner lining, or intima, of the blood vessel and with the blood. A stent made of wire mesh, when inserted into the blood vessel, tends to allow growth of the intima between and through the mesh. Such growth, or neointimal proliferation, can constrict or close the channel that the stent is intended to provide. Stents with two layers of mesh and a PTFE layer in between have been used, but these have all included a portion of the wire mesh extending beyond the ends of the PTFE layer, providing an area for neointimal proliferation.
The stents with two layers of mesh with a PTFE layer in between have a disadvantage produced by the outer mesh layer's directly contacting the intima. The direct exposure of the intima to the metal of the mesh layer may promote embolic events and restenosis. Expansion of the stent into place in the blood vessel, in particular at an area of stenosis caused by plaque, can disturb and break away small pieces of plaque or emboli, raising the risk of embolism if the emboli are allowed to travel downstream in the blood.